1. Field of the Invention
The present invention generally relates to an image forming apparatus, and more particularly, to fusing equipment of an electro-photographic image forming apparatus for fixing an image transferred thereto onto a paper.
2. Description of the Related Art
Generally, an electro-photographic image forming apparatus has a photosensitive drum that receives digital image signals from a laser scanning unit (LSU) and forms an electrostatic latent image accordingly, a developing unit that develops the electrostatic latent image of the photosensitive drum with a developing agent (hereinafter called ‘toner’), and a transfer unit that transfers the developed image formed on the photosensitive drum onto a recording paper.
The transfer unit includes fusing equipment. The fusing equipment fixes the toner onto a printing medium with heat and pressure.
FIG. 1 shows conventional fusing equipment for use in an image forming apparatus. As shown in FIG. 1, the conventional fusing equipment includes a fusing roller 80 formed on an upper portion of the fusing equipment, a pressing roller 96 formed on a lower portion of the fusing equipment, and a thermistor 82 that detects a surface temperature of the fusing roller 80.
The fusing roller 80 includes a heating lamp 86 formed in a center portion of the fusing roller 80, an air layer 88 surrounding the heating lamp 86, a supporting layer 90 supporting the fusing roller 80, a resilient layer 92 formed of resilient material and surrounding the supporting layer 90, and a separating layer 94 surrounding the resilient layer 92. A halogen lamp is usually used as the heating lamp 86.
The pressing roller 96 rotates while being in contact with the separating layer 94 with an intervention of printing paper 99 therebetween. The pressing roller 96 is forced upward against the fusing roller 80 by a compression spring 98.
The thermistor 82 is in contact with the surface of the fusing roller 80, and detects the temperature of the rotating fusing roller 80. The fusing roller 80 fixes toner 95 on the printing paper 99 when the printing paper passes between the fusing roller 80 and the pressing roller 96.
In the conventional fusing equipment, radiation heat generated from the heating lamp 86 is transmitted to the supporting layer 90 via the air layer 88 and then transmitted through the resilient layer 92 to the separating layer 94, thereby transmitting the radiation heat to the printing paper 99.
At room temperature, a sufficient amount of heat is not quickly transmitted to the surface of the fusing roller 80 to melt the toner 95. Although there are differences in a melting point (temperature) of respective toner types of the toner 95 and a structure of the fusing equipment, it generally takes a longer period of time to warm up the fusing roller 80. When power is just turned on or when the printer is in a sleep state, it takes from about 30 seconds to about 1 minute for a mono laser beam printer (LBP), or from about 3 minutes to about 5 minutes for a color laser beam printer (CLBP) to be in a standby state, i.e., to be warmed-up for printing.
The printer enters into the sleep state to save energy consumption when there is no printing command for a long time. In the sleep state, the power to a heat source of the fusing roller 80 is cut off, thereby maintaining a fusing roller temperature at the room temperature. Then the printer enters into a standby state to be supplied with the printing paper. In the standby state, the fusing roller temperature is maintained at a lowest level that can be increased to a printing temperature allowing the printing at a maximum speed.
As mentioned above, it takes a lengthy time for the conventional fusing equipment to be warmed-up because it usually employs the halogen lamp as the heat source and is constructed in such a manner that the heating lamp 86 is heated inside of the supporting layer 90 of the fusing roller 80 to heat up the fusing roller 80 through the air layer 88.
Further, even though the supporting layer 90 is heated by the heat source, it takes a considerable time that the heat reaches the separating layer 94 disposed at the outer most side of the fusing roller 80 because the resilient layer 92, which surrounds the supporting layer 90, is made of materials of a low heat conductivity, such as a rubber.
Meanwhile, because the thermistor 82 is formed on an outside of the fusing roller 82 and is in contact with the surface of the separating layer 94, the thermistor 82 can be attached with foreign substances, such as dirt and dust. As a result, especially when it is used for a long time, the thermistor 82 would detect the surface temperature of the fusing roller inaccurately.